Getting Started with a Continuous Glucose Monitor (CGM)
If you have type 1 diabetes, you test your blood glucose – also known as blood sugar – levels multiple times per day and use those levels to help adjust your insulin dosage. While glucose testing has become easier and less painful with new glucose meters, it still involves multiple finger pricks per day.
A traditional glucose meter gives you a snapshot of where your glucose level is at the time of testing, but it doesn’t tell you whether your blood sugar is going up or down, or the speed and rate of change.
Typically, insurance and HMOs also cover the cost of just a few test strips per day. If you want to test frequently to achieve careful glycemic control, you must pay out of pocket for extra strips—and they are expensive!
An alternative is a continuous glucose monitor, or CGM, device. CGMs are FDA-approved and have a tiny filament sensor inserted under the skin. The sensor reads your glucose level every five minutes throughout the day and night. The sensor is attached to a small transmitter that is taped to your skin, usually on the abdomen. The transmitter sends your glucose levels wirelessly to a small separate monitoring device, your smartphone, a smartwatch (like an Apple watch), or a tablet computer.
A CGM not only gives you the glucose level, but tells you if that level is rising or falling, and the speed of those changes. A CGM also allows you to set audible alarms that go off at designated high or low blood glucose cutoff points.
Benefits of a CGM
Studies have shown that when used consistently, a traditional CGM device can help you achieve tighter control of your diabetes. The benefits include:
Reduced risk of hypoglycemia (low blood glucose level) or hyperglycemia (high blood glucose level)
Fewer finger sticks per day
Nighttime monitoring – with loud audible alerts to wake you up if you become hypoglycemic
A better understanding of the impact of different foods, physical activity, stress, and medications on your blood glucose level
The ability to enter meals, physical activity, medications, and insulin doses into the CGM, for tracking and reporting purposes
The ability to upload data to an application for review, and to produce reports that you, your doctor, or your diabetes educator can use to help achieve better control of your diabetes
Most models allow you to send urgent high or low blood sugar notifications to another person’s smartphone. This is particularly helpful for parents, caregivers, and partners of people with diabetes.
The alert functions of a CGM are also useful if you frequently have hypoglycemic events, or you are unaware when your blood sugar is dangerously low, especially if it occurs at night while you’re sleeping. A CGM is also helpful for controlling blood sugar during pregnancy, a time when it is important to have optimal diabetes management.
Using a CGM
A CGM is either a stand-alone device or is integrated into an insulin pump.
With a traditional CGM, you insert the ultra-thin filament sensor into your abdomen. You may feel a minor prick, but it usually painless. A tiny transmitter is then attached to the sensor externally, usually with an adhesive pad on your abdomen.
Once your sensor has warmed up, you typically need to calibrate your CGM by taking a traditional finger prick blood glucose level and entering it into your CGM. You will usually need to calibrate with a finger prick every 12 hours. Sensors usually last from a week to ten days, after which they need to be replaced. The transmitter itself typically needs to be replaced every several months. Check with the manufacturer for specific timeframes for each device.
Type of CGMs and their costs
CGMs are only available with a doctor’s prescription. If you have type 1 diabetes, you should find it easier to get insurance or HMO coverage for a CGM. If you have type 2 diabetes that is poorly controlled, or you require insulin therapy, you may be able to have your physician make a case to your health insurer to get a CGM as part of your treatment.
One popular stand-alone CGM device is the Dexcom G5. Dexcom is frequently covered by health insurers and HMOs as well as Medicare. The retail cost for a Dexcom G5 is typically from $700 to $1,200. Sensors can cost approximately $300 a month.
The Medtronic Minimed is a combined insulin pump/CGM, and the retail cost is approximately $7, 500 for the pump/CGM system, not including sensors. Insurance copays can run up to $1,500 for a Minimed pump/CGM.
The American Diabetes Association has a helpful comparison chart, showing the features of the different devices.
A newer CGM on the market is the Freestyle Libre, made by Abbott. This lower-cost, stand-alone CGM was released in late 2017. The one-time purchase of the Freestyle Libre reader device ranges from $70 to $100, and 10-day sensors run from $36 to $55, or $102 to $165 a month.
More expensive CGMS like Dexcom and Minimed read blood sugar every 5 minutes, and automatically send audible alerts for blood sugar highs, lows, and rapid increases and drops. The Freestyle Libre requires the user to pass a receiver over the transmitter site in order to take a reading. The transmitter does not automatically read and report blood sugar levels or send alerts.
As of early 2018, the Freestyle Libre is not currently covered by health insurance, but Medicare does cover the Freestyle Libre for certain seniors, namely those with type 1 diabetes, or those who receive "intensive insulin therapy for type 2 diabetes," and require "frequent insulin dosing adjustments, based on checking blood glucose levels at least 4 times a day."
It is expected that health insurance coverage will be extended sometime in 2018. The retail cost, however, is so much less than the retail cost or copay amount for other CGM devices that some patients are opting for the Freestyle Libre as an affordable CGM option.
Some considerations about your CGM
You can wear your CGM when sleeping, bathing, showering, swimming, or exercising. (Note, however, that while submerged underwater, your meter’s ability to transmit may be temporarily interrupted.)
If you take medications that contain acetaminophen (i.e., Tylenol) while wearing your CGM, you may get false readings, typically high blood glucose readings. You can either use an alternative medication or use your regular glucose meter while taking acetaminophen.
When traveling, it’s considered safe to go through both x-ray and body scanners wearing your CGM. Manufacturers do recommend, however, that you ask for hand inspection of any extra sensors or transmitters that you may be carrying, and do not put them in your checked luggage where they may be subject to x-rays.
Can a CGM be used to manage type 2 diabetes?
While CGMs are typically used for type 1 diabetes, if you have type 2 diabetes, a CGM could be useful in helping you achieve better glucose control. Research shows that CGMs are useful for type 2 diabetes patients on insulin therapy. A CGM can also provide far more in-depth information on the effect of various foods and physical activities on your blood sugar levels. The data from your CGM can help you make dietary and lifestyle adjustments that can help you better control your blood glucose levels.
One study of people with type 2 diabetes found that those using a CGM, compared to self-monitoring, were able to reduce their caloric intake, lose weight, and reduce their AIC levels more effectively. In another study, over a six month period, the CGM-users with type 2 diabetes were able to reduce their AIC level by almost 2 percent, from 8.9 to 7.
My CGM experience
I was diagnosed with latent autoimmune diabetes in adults (LADA), a form of type 1 insulin-dependent diabetes, in early 2017. For part of the year, I did traditional finger prick glucose testing but started using a CGM to manage my type 1 diabetes in the fall of 2017. My doctor prescribed the Dexcom G5 CGM, and I’ve been using it for almost 6 months.
It took about an hour with my diabetes educator to learn how to insert the sensor and how to use the monitoring data. I get the data on my trusty iPhone, which is always with me. Once I got the hang of it, it’s become second nature to check in to my CGM results regularly and adjust accordingly. I barely notice the transmitter, and it's not visible through most clothing.
With my CGM, I've been able to keep much better control of my blood sugar levels and have far fewer hypoglycemic episodes. I had a significant drop in my AIC level from 7.1 to around 6.1, reflecting improved glycemic control.
I also have a better awareness of how different foods affect my blood sugar and I am able to use my insulin more effectively. I can’t imagine going back to multiple finger pricks during the day or having no sense of how my blood sugar is trending. If you have diabetes, I highly recommend that you explore the option of a CGM with your health care provider!